1. Field of the Invention
This invention relates to a device for mounting a magnetic roller which is disposed in a developing unit of a copying apparatus, such as a copying machine or a laser beam printer, and more particularly, to a device for mounting the magnetic roller to prevent an overflow of toner while constantly maintaining a given distance between the magnetic roller and a drum.
2. Discussion of the Related Art
A copying apparatus, such as a copying machine or a laser beam printer, is shown in FIG. 1 of the accompanying drawings. The copying apparatus of FIG. 1 comprises a charging unit 2 for applying an electric charge to a peripheral surface of a drum 1, a developing unit 4 for applying toner to an electric latent image formed on the drum 1 by a light incident on the drum 1 through a lens portion 3, a transfer unit 5 for transferring and attaching the applied toner to a copying paper, and a toner recovery unit 6 for recovering toner waste attached to the drum 1. The units are disposed around the drum 1. In the copying apparatus of FIG. 1, printing is accomplished by feeding a paper 8 from a paper feed tray 7 which passes between the drum 1 and the transfer unit 5, and then through a fixing unit 9.
With this construction, the developing unit 4 plays an especially important role of feeding the toner in the form of fine powder to the drum 1 to apply the toner on the latent image on the drum 1 at a constant thickness. In order to uniformly apply the toner, which is stored in a toner box of the developing unit 4, on the drum, a magnetic roller is provided inside the toner box with a magnet and maintained at a given distance from the surface of the drum to set the thickness of a toner coating.
In the past, as shown in FIGS. 2 and 3 of the accompanying drawings, the magnetic roller 11 has been disposed in the toner box 15 through a pair of opposite swing arm brackets 10. Each of the brackets 10 is coupled at one end to a shaft of the magnetic roller 11 and fixedly secured at the other end to a hinge rod 12 which is disposed parallel to the magnetic roller 11 and pivotally supported on the opposite sidewalls of the toner box 15. Collars 14, each having a diameter larger than that of the magnetic roller 11, are secured to the shaft of the magnetic roller 11 at respective outer surfaces of the swing arm brackets 10. Springs 13 are each disposed about the hinge rod 12 between the outer surface of each bracket 10 and the inner surface of each sidewall of the toner box 15.
With this arrangement, the swing arm brackets 10 are normally urged, under the resiliency of the springs 13, to rotate about the hinge rod 12 in a counterclockwise direction (as viewed in the drawings), so that the collars 14 are kept in direct contact with the drum 1. Due to a difference in diameter between the collar 14 and the magnetic roller 11 (the collar being larger than the magnetic roller), a spacing between the drum 1 and the magnetic roller 11 is defined.
The conventional device as mentioned above may constantly maintain the given distance between the drum 1 and the magnetic roller 11 without any difficulty. However, since the swing arm brackets 10 disposed in the toner box 15 must be mounted spaced apart from the toner box for their operation, the device encounters a problem in which the toner may overflow through the spacing.
Therefore, the conventional device is disadvantageous, in that, since the freely movable mounting of the swing arm brackets 10 in the toner box 15 requires a spacing between the brackets and the toner box, the toner may flow out of the toner box through the spacing. When the toner flows out of the toner box, the machine becomes polluted and the performance is reduced.